1. Technical Field
The present invention relates to a routing protocol, and more particularly, to a method for selecting an optimum route by reflecting network changes in a routing protocol.
2. Related Art
A routing protocol is a communication regulation for network routing, and determines a route among devices (e.g., routers) organizing a network. For example, the routers designate an optimum route for packets by referring to a pre-stored routing table when there is a packet transmission request. The routing protocol is a protocol for delivering information (e.g., routing information) for updating the routing table among the routers.
Since the Internet has recently expanded extensively, it is difficult to update routing tables of all routers using one routing protocol. Thus, the Internet has been divided into autonomous systems (AS) operated by one management authority, and separate routing protocols are used for inner routing in respective autonomous systems and for outer routing between the autonomous systems, respectively.
The protocols most commonly used as an inner routing protocol and an outer routing protocol include a routing information protocol (RIP) and an open shortest path first (OSPF) as inner routing protocols, and a border gateway protocol (BGP) as an outer routing protocol.
RIP is a protocol using a distance vector algorithm which dynamically determines a shortest route depending on hop counts of the routers through which the RIP passes. OSPF is a protocol which supports routing through the shortest route by combining inter-node distance information and link status information with the routing information in real time so that users select the shortest route in an Internet network. BGP is a protocol for the exchange of routing information among gateway hosts in the network of the Autonomous System.
Recently, as the scale of a network has expanded, routing protocols have been getting more important for increasing transmission efficiency of the network. In other words, how quickly the routing protocol selects an optimum route by reflecting changes on the network has become a key factor. Conventional routing protocols, however, have focused on transmission reliability rather than processing speed. Moreover, the conventional routing protocols have been unable to adapt to changes on the network in selecting the optimum routing path. For example, BGP, as a protocol, has focused on how to reliably transmit routing information to neighboring routers, and thus it is relatively poor when it comes to updating the routing information through a fast route.
If one of the ASs (hereinafter, referred to as receiving AS) transmitting routing information using the BGP receives a plurality of the same route information from different neighboring ASs (hereinafter, referred to as transmitting ASs), the receiving AS determines whether the transmitting ASs have the same hop count. That is, the receiving AS determines whether the different neighboring ASs transmitting the same route information have the same hop count. As a result of that determination, if it is determined that the transmitting ASs have the same hop count, the receiving AS establishes an optimum route using the earliest received route information. Otherwise, the receiving AS establishes the optimum route using route information which is received from the AS having a smaller hop count than the receiving AS.
On the other hand, if it is determined that the receiving AS has not received the same route information from a plurality of different neighboring ASs, but has received different route information from different neighboring ASs, the receiving AS establishes the route using the received route information.
Presuming that AS1, AS2 and AS3 are connected to network A and transmit routing information using BGP, AS3 calculates the hop counts of AS1 and AS2 when receiving the same route information from AS1 and AS2. This is accomplished so that AS3 can select an optimum route using the route information of whichever one of AS1 and AS2 has the smaller hop count.
However, AS1 and AS3, and AS1 and AS2, are interconnected via the same number of routes. AS3 and AS1 are interconnected via a first router R1 and a second router R2. AS3 and AS2 are interconnected via a third router R3 and a fourth router R4. Therefore, from the viewpoint of AS3, AS1 and AS2 have the same hop count.
In this case, AS3 establishes an optimum route using whichever one of the route information from AS1 or the route information from AS2 is received earlier. For instance, if AS3 receives the route information from AS2 after receiving the route information from AS1, AS3 establishes the optimum route using the route information received from AS1. However, if the transmission speed of a route from AS1 to AS3 (hereinafter, referred to as the first route) is slower than that of a route from AS2 to AS3(hereinafter, referred to as the second route) due to network traffic on the first route, it is an optimal selection for AS3 to select AS2 as the next hop. However, AS3 selects AS1 as the next hop based on the above-mentioned criteria. In other words, AS3 selects AS1 as the next hop because AS1 transmitted the route information first.
As mentioned above, there is a disadvantage in that the conventional routing protocols are unable to properly reflect changes on the network in selecting an optimum routing route. That is, there is a disadvantage in that the conventional routing protocols cause an error in selecting an optimum route because they select the optimum route without reflecting traffic volume on each link on a network.